1. Field of the Invention
The invention relates generally to an intervertebral spacer and method for spacing and fusing adjacent vertebrae and, more particularly, to a porous, strong, intervertebral spacer formed of a biologically inert material.
2. Description of the Prior Art
Techniques and devices for fusing two or more vertebrae of the spine together are well known. Such techniques are commonly performed to correct problems, such as chronic back pain, which result from degenerated intervertebral discs. One technique for fusing together two or more vertebrae of the lumbar spine includes excising a portion of the disc extending between adjacent vertebrae and grafting one or more portions of bone of a desired shape, known as an intervertebral spacer, between the adjacent vertebrae. The intervertebral spacer may be inserted by either an anterior or posterior approach to the spinal column depending on a number of factors, including the number of vertebrae to be fused and past operative procedures. Upon healing, the vertebrae are desirably fused together through the intervertebral spacer.
Conventionally, intervertebral spacers have been autogenic bone harvested from other areas of the body, such as the pelvis, allogenic bone taken from cadavers or xenogenic bone, such as bovine bone sections. However, the use of bone grafts can add complications to the fusion procedure. For example, when using an autogenic bone graft, a second incision must be made in the patient to harvest the additional bone to be used in the graft, thus increasing the pain and blood loss to the patient. When allogenic or xenogenic bone grafts are used there is a potential for the transmission of disease from the cadaver or other graft source to the patient.
The use of non-biological implants, such as carbon fiber spacers, also has been attempted in the past, but these spacers tend to lack sufficient porosity and tissue ingrowth characteristics to function adequately.
It would be desirable to provide a non-biological spacer which is non-reactive in the body and which has the strength and tissue ingrowth characteristics of a bone graft spacer.
The present invention provides a porous intervertebral spacer which can be used in the same manner as a bone graft spacer to fuse vertebrae together. The inventive spacer preferably is composed biologically inert strands, or a mixture of such strands and biologically inert beads sintered in a mold of a desired shape and size. The spacer is made of metals such as titanium, and thus is non-biologically reactive and provides for tissue ingrowth to facilitate fusion with adjacent vertebrae.
In accordance with one aspect of the invention, a porous intervertebral spacer is formed in a variety of shapes such as a prism (for example, a rectangular prism), a cylinder, and a plate. In each instance, the spacer is made of a plurality of fused, tortuous strands or a mixture of tortuous strands and beads of a biologically inert material such as titanium or a titanium alloy.
In accordance with another aspect of the invention a method of fusing adjacent vertebrae of the spine includes the steps of excising a portion of an intervertebral disc separating adjacent vertebra and portions of the adjacent vertebrae to define a graft bed, and inserting into the graft bed at least one porous intervertebral spacer formed from a plurality of fused, tortuous strands or a mixture of tortuous strands and beads of a biologically inert material such as titanium or a titanium alloy.